1) Field of the Invention
The present invention relates to a light reflecting plate suitable for use in reflection type liquid crystal display devices, a production process thereof and a reflection type liquid crystal display device making good use of the light reflecting plate.
2) Description of the Related Art
Liquid crystal display devices are used in very various fields as displays for televisions, personal computer (PC) monitors, note type PC, pen-input PC, mobile PC, handheld game machines, digital cameras, cellular phones, etc., because they are light weight, thin and low electric power. Among these, with respect to the uses that attach great importance to portability, the so-call reflection type that external light is utilized for elongating the life of a battery quickly increases. In each of these reflection type liquid crystal display device, a light reflecting plate is arranged on the back surface of a liquid crystal, external light struck from the front side of each display device is reflected on the light reflecting plate to display it as an image to a viewer. These displays are roughly divided into a type that a reflecting plate is provided on the external side of a liquid crystal cell with a liquid crystal layer held between a pair of transparent substrates opposed to each other and each having a display electrode on the internal side thereof, and a type that a light reflection layer is provided on the side of one display electrode within the liquid crystal cell.
The typical construction of the former type that the reflecting plate is provided on the external side of the liquid crystal cell is illustrated in FIG. 10. The liquid crystal cell is constructed by arranging a glass plate on one side of which a polarizing plate is provided and on the other side of which a transparent electrode is provided through a color filter, and a glass plate on one side of which a polarizing plate is provided and on the other side of which a transparent electrode is provided in such a manner that a liquid crystal is held between both transparent electrodes to form a liquid crystal layer. The reflecting plate is provided on the polarizing plate on the latter glass plate.
With respect to this display device, description is given by taking a TN liquid crystal the orientation direction of which is twisted by 90xc2x0 between the upper and lower sides as an example. In the case where no voltage is applied, external light Ai passes through the polarizing plate, liquid crystal and polarizing plate and is reflected on the reflecting plate, and the reflected light passes through the polarizing plate, liquid crystal and polarizing plate and is discharged from the display device as Ar. On the other hand, when voltage is applied to the liquid crystal, external light Bi is incident through the same optical path as described above. However, the incident light is absorbed in the lower-side polarizing plate, and a part thereof is reflected. However, the reflected light is also absorbed in the upper-side polarizing plate. Therefore, outgoing light Br is scarcely observed, and so the reflected light from the display device can be viewed as an image.
By the way, as the reflecting plate essential for such a reflection type liquid crystal display device, is used a plate of a metal such as aluminum or a synthetic resin film deposited with a metal. When the metal surface of the reflecting plate is flat, however, the reflecting plate has involved problems that regular reflection is strong, and so an angle of field is narrow, and the visibility of an image formed is deteriorated because the glossy color of the metal as a ground is seen. Therefore, it is conducted to reduce the metallic gloss by mechanically rubbing the surface of an aluminum foil with a rotating brush to provide hairlines on the surface or depositing a metal on a matte-treated synthetic resin film. However, the effects thereof are not sufficient. Japanese Patent Application Laid-Open No. 158237/1982 has proposed an example that a metal deposited film is formed on a resin film containing an extremely fine particulate substance, Japanese Patent Application Laid-Open No. 79497/1978 an example that aluminum is deposited on an irregular surface composed of glass beads embedded in or bonded to a substrate, and Japanese Patent Application Laid-Open No. 151989/1982 an example that glass beads are attached to a thermoplastic resin layer in a state softened by a heated roll and surely stuck by reheating, and a metallic reflecting film is then formed on the surface thereof. However, these publications do not sufficiently show respective components and light-diffusive performance of the reflecting films, and so the action and effects thereof are indefinite. Therefore, it is hard to consider that all the proposals permit providing reflecting films having fixed reflection properties with good reproducibility. Further, Japanese Patent Application Laid-Open No. 258901/1992 discloses an example that a metal layer is provided on a coating layer formed of spherical fine particles and a binder, and Japanese Patent registration No. 3092035 an example that spherical fine beads are uniformly dispersed on the surface of a resin film or sheet, a transparent resin binder is filled between adjacent beads, and a thin metal film having a high reflectivity is then formed on the surface thereof. In any example, however, intervals among the spherical fine particles or beads which form irregularities, by which the light diffusion properties of the reflecting film are determined, cannot be sufficiently controlled, and so it is extremely difficult to provide reflecting films with good reproducibility.
On the other hand, the type that the light reflection layer is provided on the side of one display electrode within the liquid crystal cell can decrease one polarizing plate to brighten an image formed and can solve a problem of a twin image due to parallax. Therefore, the development of such a type has been recently advanced. The typical construction thereof is illustrated in FIG. 11. This liquid crystal cell has construction that a polarizing plate, a phase difference plate, a glass plate, a color filter, a transparent electrode, a liquid crystal layer, a reflecting electrode and a glass plate are laminated in that order. The reflecting electrode shown herein combines a display electrode function with a light reflecting function.
When the reflecting electrode is specular in the reflection type liquid crystal display device of this type, it is conducted to provide a light diffusing layer or a light diffusing film on the surface of the polarizing plate or between the polarizing plate and the phase difference plate, or the glass plate and the phase difference plate Japanese Patent Application Laid-Open Nos. 57084/1981, 104272/1995 and 161110/1998 show such cases. These cases involve problems that cost is increased by a share of the provision of the light diffusing layer or the light diffusing film, and moreover that the brightness and contrast of an image formed are lowered when it is intended to reduce the metallic gloss of the reflecting electrode. It is also conducted to provide irregularities in the reflecting electrode itself to impart light diffusing properties thereto. There have been known, for examples, a method in which a heat, honing or etching treatment is conducted after formation of a reflecting layer, an example that a reflecting layer is formed after a honing treatment, which is disclosed in Japanese Patent Application Laid-Open No. 212931/1992, and an example that a reflecting layer is provided after irregularities are formed by electron beam deposition. CVD or plasma CVD, which is disclosed in Japanese Patent Application Laid-Open No. 315129/1992. However, these cases have involved a problem that the treatments thereof are complicated, and so it is difficult to control the degree of the irregularities with good reproducibility. In addition, Japanese Patent Application Laid-Open Nos. 267220/1992 and 308816/1992 disclose an example that a thin metal film is provided on irregularities formed by applying an organic insulating film to which fine particles have been added. The mere application of a coating containing the fine particles fails to uniformly arrange the fine particles at a high density like the typical drawings shown in these publications. Accordingly, it is difficult to achieve reflection properties uniform and high in reproducibility.
As described above, both cases where the reflecting plate is arranged on the external side of the liquid crystal cell and where the reflecting electrode is provided within the liquid crystal cell have not yet come to realize paper white by completely losing the metallic gloss, and moreover it has been difficult to achieve the production stability thereof, i.e., to produce a reflecting plate or a reflecting electrode having uniform and fixed reflection properties with high reproducibility. In the reflection type liquid crystal display device, the dependency of preferable reflected light on angle varies according to the kind and use application of the liquid crystal display. However, it has been difficult to produce a reflecting plate having such many reflection properties by a simple technique in the prior art.
The present invention has been made in view of the foregoing circumstances in the prior art.
Accordingly, it is an object of the present invention to provide a reflecting plate for a reflection type liquid crystal display device capable of reproducing paper whiteness.
Another object of the present invention is to provide a production process of a reflecting plate, by which a reflecting plate having uniform and fixed reflection properties can be produced with good reproducibility.
A further object of the present invention is to provide a production process of a reflecting plate which can control reflection properties according to the kind of a liquid crystal display.
A still further object of the present invention is to provide a reflection type liquid crystal display device capable of reproducing paper whiteness.
According to the present invention, there is thus provided a light reflecting plate comprising a substrate, a single-layer powder coating provided on the substrate by laying powder particles in a state of a monoparticle layer on the substrate to fix them, and a thin metal film laminated on the single-layer powder coating.
In the light reflecting plate according to the present invention, the powder particles may preferably be spherical fine particles having a particle diameter of 1 to 20 xcexcm. The substrate may preferably be in the form of a plate or film. The substrate and/or the powder particles may preferably have light transmission property. The thin metal film may preferably be formed from any one metal selected from the group consisting of gold, silver, aluminum and nickel.
According to the present invention, there is also provided a process for producing the light reflecting plate described above, which comprises a step of providing a binder layer having tackiness on a substrate, a step of laying powder particles in a state of a monoparticle layer on the binder layer having tackiness to fix them, and a step of laminating a thin metal film on the single-layer powder coating formed in the late step.
In the production process described above, the step of laying the powder particles in a state of a monoparticle layer on the binder layer having tackiness to fix them may preferably be a step of bringing the substrate provided with the binder layer having tackiness into contact with the powder particles and a medium vibrated in a container.
According to the present invention, there is further provided a first liquid crystal display device comprising a liquid crystal cell with a liquid crystal layer held between a pair of transparent substrates opposed to each other and each having at least a display electrode on the internal side thereof, and a light reflecting plate reflecting incident light, which is provided on the external side of one of the transparent substrates, wherein the light reflecting plate comprises a substrate, a single-layer powder coating provided on the substrate by laying powder particles in a state of a monoparticle layer on the substrate to fix them, and a thin metal film laminated on the single-layer powder coating.
According to the present invention, there is still further provided a second liquid crystal display device comprising a liquid crystal cell with a liquid crystal layer held between a pair of transparent substrates opposed to each other and each having at least a display electrode on the internal side thereof, and a light reflecting layer reflecting incident light, which is provided on the side of one display electrode within the liquid crystal cell, wherein the light reflecting plate comprises a substrate, a single-layer powder coating formed on the substrate by laying powder particles in a state of a monoparticle layer on the substrate to fix them, and a thin metal film laminated on the single-layer powder coating.